ARTICLE UPDATE - Placebo in Emotional Processing— Induced Expectations of Anxiety Relief Activate a Generalized Modulatory Network

Predrag Petrovic, Thomas Dietrich, Peter Fransson, Jesper Andersson, Katrina Carlsson and Martin Ingvar

Neuron, 46, 957-969

Placebo analgesia and reward processing share several features. For instance, expectations have a strong influence on the subsequent emotional experience of both. Recent imaging data indicate similarities in the underlying neuronal network. We hypothesized that placebo analgesia is a special case of reward processing and that placebo treatment could modulate emotional perception in the same way as does pain perception. The behavioral part of this study indicates that placebo treatment has an effect on how subjects perceive unpleasant pictures. Furthermore, event-related fMRI demonstrated that the same modulatory network, including the rostral anterior cingulate cortex and the lateral orbitofrontal cortex, is involved in both emotional placebo and placebo analgesia. These effects were correlated with the reported placebo effect and were predicted by the amount of treatment expectation induced on a previous day. Thus, the placebo effect may be considered to be a general process of modulation induced by the subjects’ expectations.

ARTICLE UPDATE - The role of the amygdala in human fear: Automatic detection of threat

Arne Öhman

Psychoneuroendocrinology, in press

Behavioral data suggest that fear stimuli automatically activate fear and capture attention. This effect is likely to be mediated by a subcortical brain network centered on the amygdala. Consistent with this view, brain imaging studies show that masked facial stimuli activate the amygdala as do masked pictures of threatening animals such as snakes and spiders. When the stimulus conditions allow conscious processing, the amygdala response to feared stimuli is enhanced and a cortical network that includes the anterior cingulate cortex and the anterior insula is activated. However, the initial amygdala response to a fear-relevant but non-feared stimulus (e.g. pictures of spiders for a snake phobic) disappears with conscious processing and the cortical network is not recruited. Instead there is activation of the dorsolateral and orbitofrontal cortices that appears to inhibit the amygdala response. The data suggest that activation of the amygdala is mediated by a subcortical pathway, which passes through the superior colliculi and the pulvinar nucleus of the thalamus before accessing the amygdala, and which operates on low spatial frequency information.

ARTICLE UPDATE - The role of the human amygdala in the production of conditioned fear responses

David C. Knight, Hanh T. Nguyen and Peter A. Bandettini

NeuroImage, 26, 1193-1200

The amygdala plays a central role in the acquisition and expression of fear memories. Laboratory animal studies indicate that the amygdala both receives sensory information and produces learned behavioral and autonomic fear responses. However, prior functional imaging research in humans has largely focused on amygdala activity elicited by fearful stimuli, giving less attention to this region's role in the production of fear responses. In contrast, the present study used functional magnetic resonance imaging to investigate the amygdala's influence on the generation of conditional fear responses. Significant increases in amygdala activity were observed during the production of conditioned (learning-related), but not orienting, nonspecific, and unconditioned (nonlearning-related) skin conductance responses. Further, greater amygdala activity was demonstrated during conditioned response production than during conditioned stimulus presentation. These results suggest the amygdala not only responds to fearful stimuli, but also generates learning-related changes in human autonomic fear expression.

ARTICLE UPDATE - Hemodynamic responses of the amygdala, the orbitofrontal cortex and the visual cortex during a fear conditioning paradigm.

Tabbert K, Stark R, Kirsch P, Vaitl D

International Journal of Psychophysiology, 57, 15-23.

Functional magnetic resonance imaging (fMRI) studies consistently demonstrate an enhanced activation of the visual cortex in reaction to emotionally salient visual stimuli. This increase of activation is probably modulated by top-down processes, that are initiated in emotion processing structures, specifically the amygdala and the orbitofrontal cortex. In the present fMRI study, a differential fear conditioning paradigm was applied to investigate this assumed modulation. Hemodynamic responses towards a neutral visual stimulus (CS+) predicting an electrical stimulation (UCS) were compared with responses towards a neutral and unpaired stimulus (CS-). Thereby, particularly the time courses of neural responses were considered. Skin conductance measures were concurrently recorded. Our results show that the differentiation between CS+ and CS- within the amygdala and the extended visual cortex was accomplished during a late acquisition phase. In the orbitofrontal cortex the differentiation occurred at an earlier stage and was then sustained throughout acquisition. It is suggested that these altering activation patterns are reflecting different phases of learning, integrating the analyzed regions to varying degrees. Additionally, the results indicate that statistical analyses comprising a temporal variation of hemodynamic responses are more likely to detect amygdala activation.

ARTICLE UPDATE - Stimulus type and design influence hemodynamic responses towards visual disgust and fear elicitors.

Schafer A, Schienle A, Vaitl D.

International Journal of Psychophysiology, 57, 53-59.

The question to what extent emotion-related brain activation depends upon the presentation design (block design vs. event-related design) and the stimulus type (scene pictures vs. pictures with facial mimic) has hardly been addressed in previous functional magnetic resonance imaging (fMRI) research. In the present fMRI experiment, 40 right-handed subjects viewed pictures with fear-inducing and disgust-inducing content as well as facial expressions of fear and disgust. Pictures of neutral objects and neutral facial mimic were used as control stimuli. The pictures were presented in a block design for half of the subjects; the other half viewed the same stimuli as singular events in randomized sequence. The participants had been instructed to passively view the pictures. Disgust-evoking scenes provoked activation in the amygdala, the insula and the orbitofrontal cortex (OFC). This applied to the blocked as well as to the event-related design. Fear-relevant scenes were associated with activity in the insula, the OFC and the middle temporal gyri in the event-related design. The presentation in a block design only led to activation in the middle temporal gyri. Facial expressions of disgust and fear did not trigger significant activation neither in the blocked nor event-related design. This surprising outcome may be a result of context and task effects. The face stimuli which were presented together with the more complex scenes in a passive viewing paradigm possibly were not salient enough to trigger emotional processing.